Mobile robots are increasingly commonplace and are used in such diverse fields as space exploration, lawn mowing and floor cleaning. The last decade has seen particularly rapid advancement in the field of robotic floor cleaning devices, especially vacuum cleaners, the primary objective of which is to navigate a user's home autonomously and unobtrusively whilst cleaning the floor. The invention will be described in the context of a robotic vacuum cleaner but it is also applicable in general to any type of mobile robot platform, such as robotic lawn mowers.
Common to all mobile robots is the requirement for a drive system. In the context of robotic floor cleaners, a popular approach is to provide the robot body with wheel on each side, each wheel being drivable independently. Therefore, the robot can move linearly by driving both wheels in the same direction at the same speed or can turn by varying the relative rotation of the wheels. Driving both wheels in opposite direction enables the robot to rotate on the spot. Such a system usually will also include a third wheel positioned towards the rear of the robot body which acts as a caster, passively rolling along whilst providing a support for one side of the body. A significant advantage of such a system is that it makes the robot highly maneuverable and also avoids the need for an additional steering mechanism. Examples of autonomous robotic vacuum cleaners using such a drive arrangement are Roomba™ by iRobot and Trilobite™ by Electrolux.
A disadvantage of the wheeled mobile robot as described above is its limited ability to climb over objects, or even over or onto floor coverings such as cables or rugs.
An alternative approach is to equip an autonomous floor cleaner with a tracked drive arrangement, as shown in European patent application no. EP1582132. Such an arrangement tends to improve grip due to the larger contact patch inherent with a track and so it may be better at negotiating obstacles such as rugs and cables. However, due to the increased contact patch the robot drive system is more susceptible to slippage which is a disadvantage because it introduces inaccuracies into the navigation system of the robot.